The rate at which a Frame Relaynetwork agrees to transfer information under normal conditions,averaged over a minimum increment of time. CIR, measured in bits persecond, is one of the key negotiated tariff metrics.

Local access rate

-

The clock speed (port speed) of the connection (localloop) to the Frame Relay cloud. It is the rate at which data travels intoor out of the network.

Committed Burst

(Bc)-

The maximum number of bits that the switchagrees to transfer during any Committed Rate Measurement Interval(Tc).

Excess Burst

-

The maximum number of uncommitted bits that theFrame Relay switch will attempt to transfer beyond the CIR. ExcessBurst is dependent on the service offerings available by your vendor,but is typically limited to the port speed of the local access loop.

Glossary

ECN

(Forward explicit congestion notification)-

When aFrame Relay switch recognizes congestion in the network,it sends an FECN packet to the destination deviceindicating that congestion has occurred.

BECN

(Backward explicit congestion notification)-

When aFrame Relay switch recognizes congestion in the network,it sends a BECN packet to the source router instructing therouter to reduce the rate at which it is sending packets.

DE

(Discard Eligibility indicator)-

When the router detectsnetwork congestion, the FR switch will drop packets withtheDE bit

set first. TheDE bit

is set on the oversubscribedtraffic; that is, the traffic that was received after the CIRwas met.

More Terms

(Three Phases)

1.Connection

Establishment

–a single path between source and destination devices isdetermined

–resources reserved to ensure a consistent rate of service

2.Data

Transfer

–data transmitted sequentially over the established path

–packets arrive at the destination in the order sent

3.Connection

Termination

–terminate the connection between source and destination

Connection-Oriented Services

Frame Relay'without'

SubInterfaces:

•Early implementation of Frame Relay Technology requiredthat a router (DTE device) must have a WAN serialinterface for every (PVC) permanent virtual circuit.

Frame Relay SubInterfaces:

•Subinterfaces

are required to configuremultiple

DLCIs

on asingle

router

interface.

•This involves logicallydividing

asingle

physical WAN serialinterface

into

multiple

virtualsubinterfaces

•A single router interface can now service many remotelocations through individual unique suberinterfaces

•Eachsubinterface

is considered aunique

network

and aunique

DLCI

number

Subinterfaces

Reachability Issues with Routing Updates

Reducing

routingloops

by:

•Split

Horizon

-

Routing updates received at central router cannot beadvertised out the same physical interface to other routers.

•Not a problem if there is only a single PVC on a physical interface,because this would be more of a point-to-point connection type.

•When running multiple PVCs over a single physical interface, this canbe a big issue.